The Co-operative group today declared itself to be Britain's first major retailer to switch completely to green electricity.

Energy for all the company's mainland sites, from more than 3,000 retail shops to its headquarters in Manchester, is now sourced from renewable energy.

"Our customers and members expect us to take a leading position in tackling climate change impacts," said Martin Beaumont, the chief executive. "By choosing this approach we want our customers to benefit from a high quality shopping experience, which also addresses much wider environmental issues."

Today's announcement is the latest salvo in the supermarket wars as they take on an increasingly green tinge. In switching entirely to renewable electricity, the Co-op has gone further than its rivals in playing the environmental card.

Asda this week announced plans to sponsor the Green Awards. Backed by the UN Environment Programme, the Green Awards seek to showcase sustainable development through marketing and communications.

Tesco, Britain's biggest supermarket chain, earlier this month said it would offer its customers one Clubcard point for every carrier bag they do not use. Clubcard points are usually awarded at a rate of one for each £1 spent.

In May, Tesco unveiled a £100m fund to test more fuel-efficient technology, such as wind turbines and solar panels, as part of a new 10-point community plan designed to reinvent the giant grocer as a "good neighbour".

The Co-op said it wanted to lead by example instead of just talking about being environmentally friendly.

"All businesses need to undoubtedly address their impacts on climate change, but for a member-owned co-operative it's an imperative," Mr Beaumont said.

The Co-op has signed a three-year agreement with Scottish Power that guarantees supplies of green electricity for all its smaller sites, including retail stores, pharmacies, farm, travel, and funeral outlets.

All the Co-op's major sites and distribution centres, which are subject to a separate arrangement, also use green power, as does Co-operative Financial Services (CFS), which includes the Co-operative Bank and Co-operative Insurance (CIS).

At the Manchester head office, the company has fitted solar panels over the 400 ft CIS building in the largest photo-voltaic project of its kind in Europe. The Co-op has also created Britain's biggest inner-city wind farm with 19 micro-wind turbines at another of its office sites in Manchester.